Conventionally, in optical communication, wavelength division multiplex (WDM) networks that transmit WDM optical signals are used (see, for example, Japanese Laid-Open Patent Publication Nos. 2006-87062, 2008-503921, and 2010-98545). In WDM networks, optical add-drop devices such as optical add-drop multiplexers (OADM) and reconfigurable-OADMs (R-OADM) that add and/or drop optical signals according to wavelength are used. In optical add/drop devices, wavelength selective switches that switch the path of optical signals, according to channel are used.
Functions for efficiently and flexibly building, modifying, and managing WDM networks is demanded of optical add-drop devices. For example, functions enabling wavelength dependency (colored), direction dependency (directional), and collision of identical wavelengths (contention) among nodes to be avoided is demanded of optical add-drop devices. Such functions are called colorless, directionless, contentionless (CDC) functions.
Colorless describes a function of being able to input an arbitrary wavelength into an arbitrary port of an optical add-drop device and to output an arbitrary wavelength from an arbitrary output. Directionless describes a function of being able to guide optical signals from terminals to an arbitrary degree and to guide optical signals from the degrees to an arbitrary terminal, in a configuration in which the optical add-drop device has multiple degrees (WDM degrees). Contentionless describes a function of being able to avoid collisions of optical signals of the same wavelength in the optical add-drop device.
Further, the following points are preferably satisfied in a configuration satisfying CDC function.
All client-side signals can be switched between wavelengths of arbitrary degrees and arbitrary wavelengths (100% add/drop capability).
From an initial operation state until the 100% add/drop state, client-side signals and the number of network-side degrees can be increased by a given unit that is as small as possible (achieving initial cost reductions and optimal cost).
When client-side signals and network-side degrees are increased, existing signals are not affected (in-service upgrade).
In an add/drop unit between a client-side signal and a network-side degree, to build a configuration that minimizes use of devices having an optical amplifying function such as an optical amplifier, a configuration that minimizes optical loss is adopted.
Since optical devices such as wavelength selective switches (WSS) and optical cross connects (OXC) are restricted in terms of optical port count, a configuration that takes into consideration the balance of port count and device count as well as optical loss is adopted.
However, with the conventional technologies above, a problem arises in that the realization of a wavelength selective switch having a large number of ports is difficult. Consequently, for example, the realization of configurations capable of implementing CDC function, having a large number of switching destinations for optical signals of each channel, etc. has been difficult.